The invention relates to a take-up device for web-shaped materials, especially plastic films with a take-up roller and a contact roller which presses the web-shaped material against the take-up roller.
Especially in the manufacture of plastic films, the plastic film webs which are stretched in a stretching system in the transverse and lengthwise direction are ultimately wound onto a take-up roller. A contact roller which presses the film layer which is outermost at the time against the rolled bale which has been wound so far is in compressive contact with the take-up roller or the rolled bale.
The known contact rollers are conventionally supported on the two roller ends. According to the working width, the required contact compressive forces and the necessary operating rpm, the diameter of the contact roller is chosen such that the desired stiffness is obtained and sagging is prevented as much as possible. At working widths from 8 to 10 m the diameter of conventional contact rollers is often more than 600 mm.
Contact rollers with large diameters however have a correspondingly great weight; this among others has an adverse effect on their dynamics and increases the friction in the bearings. Furthermore, for large diameters the contact surface which is flattened by Hertzian stress between the contact roller and the rolled bale increases so that only a limited pressure build-up is enabled on the rolled bale or very high compressive forces must be used. Furthermore the compressive force of the contact rollers with large diameters can only be influenced little over the working width and damping is sufficiently possible only on the ends of the contact roller. Large working widths have the disadvantage that the compressive force in the middle of the roller is generally too small to reliably prevent air inclusions between the individual wound layers of the take-up roller. These air inclusions however lead to nonuniform build-up of the rolled bale. Furthermore, for large working widths of the contact roller in the roller middle, running is often rough, so that concentricity is adversely affected. Problems arise with the desired width preservation effect since the material web is not uniformly pulled over its width, but is tensioned more tautly in the middle area than in the edge areas so that in this way a nonuniform build-up of the rolled bales and different hardness over the width of the rolled bale occur. In general, for the known contact rollers acquisition of information about the quality of the rolled bale is only possible to a limited degree over the ends of the contact roller.